Roll control system for a motor vehicle

ABSTRACT

( 57 ) A roll control system ( 20 ) for installation between axially aligned wheels of a motor vehicle, the roll control system comprising a torsion bar ( 22 ); a damper ( 24 ) attached to one end ( 28 ) of the torsion bar and attachable to one of the wheels; and attachment means ( 25 ) attached to the other end ( 29 ) of the torsion bar and attachable to the other wheel; wherein the damper comprises an axially extending cylindrical housing ( 52 ); a piston ( 34 ) slidably mounted inside the housing; a piston rod ( 58 ) connected to the piston, extending out of one end ( 55 ) of the housing, and movable in an axial direction relative to the housing; a floating piston ( 35 ) slidably mounted in the housing between the piston and the other end of the housing; a compensation chamber ( 37 ) between the floating piston and the other end ( 54 ) of the housing containing a first pressurised fluid; a compression chamber ( 30 ) between the floating piston and the piston containing a second pressurised fluid; a rebound chamber ( 32 ) between the piston and the one end of the housing containing the second pressurised fluid; valve means ( 36 ) on the piston allowing restricted flow of the second pressurised fluid between the compression chamber and the rebound chamber; a rebound stop ( 60 ) positioned in the rebound chamber between the piston and the one end of the housing and providing a spring-effect on the movement of the piston towards the one end of the housing; and a compression stop ( 62 ) providing a spring-effect on the movement of the piston towards the floating piston. Provides an improved passive roll controle system.

TECHNICAL FIELD

The present invention relates to a roll control system for a motorvehicle, and in particular to a passive or semi-active roll controlsystem.

BACKGROUND OF THE INVENTION

In order to prevent excessive rolling (which has an impact on vehicleattitude and handling) of a motor vehicle, especially during cornering,it is known to provide a passive roll control system comprising atorsion bar between the front wheels of a motor vehicle, and, in somecases, a second torsion bar between the rear wheels. However, duringstraight line motion of a vehicle and when the vehicle is off-road, thetorsion bar can have a detrimental effect on comfort and wheelarticulation because the torsion bar provides solely a spring effect.Semi-active roll control systems have been proposed which monitorvarious vehicle conditions. Such roll control systems include a lockingdevice associated with the torsion bar and the wheels. When the sensedvehicle conditions indicate roll stiffness is not required, the lockingdevice is unlatched to effectively disconnect the effect of the torsionbar between the wheels. When the sensed vehicle conditions indicate thatroll stiffness is required, the locking device is latched to connect thewheels by way of the torsion bar. EP-A-0829383 describes a roll controlsystem having a latch/de-latch arrangement.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improvement to theknown passive roll control systems, and, if required, adapt the passivesystem to provide a semi-active system.

A roll control system in accordance with the present invention forinstallation between axially aligned wheels of a motor vehicle comprisesa torsion bar; a damper attached to one end of the torsion bar andattachable to one of the wheels; and attachment means attached to theother end of the torsion bar and attachable to the other wheel; whereinthe damper comprises an axially extending cylindrical housing; a pistonslidably mounted inside the housing; a piston rod connected to thepiston, extending out of one end of the housing, and movable in an axialdirection relative to the housing; a floating piston slidably mounted inthe housing between the piston and the other end of the housing; acompensation chamber between the floating piston and the other end ofthe housing containing a first pressurised fluid; a compression chamberbetween the floating piston and the piston containing a secondpressurised fluid; a rebound chamber between the piston and the one endof the housing containing the second pressurised fluid; valve means onthe piston allowing restricted flow of the second pressurised fluidbetween the compression chamber and the rebound chamber; a rebound stoppositioned in the rebound chamber between the piston and the one end ofthe housing and providing a spring-effect on the movement of the pistontowards the one end of the housing; and a compression stop providing aspring-effect on the movement of the piston towards the floating piston.

The present invention provides an improved passive roll control systemin which the passive spring of a standard torsion bar is replaced by thecombined effect of a spring and damper acting together. The roll controlsystem of the present invention can be easily adapted to provide asemi-active roll control system by controlling fluid flow between thecompression and rebound chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in whic:

FIG. 1 is a schematic view of a motor vehicle having a roll controlsystem in accordance with a first embodiment of the present invention;

FIG. 2 is a perspective view of the roll control system of FIG. 1;

FIG. 3 is a schematic cross-sectional view of the damper of the rollcontrol system of FIG. 2;

FIG. 4 is a perspective view of a roll control system in accordance witha second embodiment of the present invention;

FIG. 5 is a perspective view of the roll control system in accordancewith a third embodiment of the present invention;

FIG. 6 is a cross-sectional view of the damper of the roll controlsystem of FIG. 5;

FIG. 7 is a perspective view of the roll control system in accordancewith a fourth embodiment of the present invention;

FIG. 8 is a cross-sectional view of the damper of the roll controlsystem of FIG. 7; and

FIG. 9 is a schematic of the effect on roll control of a motor vehiclehaving a roll control system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an outline of a motor vehicle 10 having a pair of frontwheels 12 and a pair of rear wheels 14. Each wheel 12,14 is rotatablymounted on an axle 16 and attached to the body of the motor vehicle 10by way of a suspension unit 18. A roll control system 20 in accordancewith a first embodiment of the present invention is connected betweenthe front wheels 12. Alternatively, a substantially identical rollcontrol system may be connected between the rear wheels 14. As a furtheralternative, substantially identical roll control systems may beconnected between the front wheels 12 and the rear wheels 14.

Referring to FIG. 2, the roll control system 20 comprises a torsion bar22, a damper 24, and a substantially rigid arm 25. The damper 24 ismounted between one end 28 of the torsion bar 22 and one of thesuspension units 18. The rigid arm 25 is mounted between the other end29 of the torsion bar 22 and the other suspension unit 18.

A preferred arrangement for the damper 24 is shown in FIG. 3. The damper24 comprises an axially extending cylindrical housing 52 which has aclosed first end 54, and a substantially closed second end 55. A piston34 makes a sealing sliding fit with the inner surface 56 of the housing52. A floating piston 35 makes a sealing sliding fit with the innersurface 56 of the housing 52 between the piston 34 and the closed firstend 54. The piston 34 defines, within the housing 52, a first(compression) chamber 30 between the piston 34 and the floating piston35, and a second (rebound) chamber 32 between the piston and the secondend 55. The floating piston 35 defines, within the housing 52, a third(compensation) chamber 37 between the floating piston and the first end54. A piston rod 58 is secured to the piston 34, extends through therebound chamber 32 and out of the second end 55 of the housing 52, andis secured to one end 28 of the torsion bar 22. The first end 54 of thehousing 52 is secured to the suspension unit 18. The piston 34 andpiston rod 58 are movable together in the axial direction relative tothe housing 52. The floating piston 35 is movable in the axial directionrelative to the housing 52.

The compensation chamber 37 contains a first pressurised fluid, forexample nitrogen. The compression chamber 30 and the rebound chamber 32contain a second pressurised fluid, such as hydraulic fluid. A valvearrangement 36 is mounted on the piston 34 which allows a restrictedflow of hydraulic fluid between the compression chamber 30 and therebound chamber 32. A rebound stop 60, preferably of elastomericmaterial, is mounted on the piston rod 58 inside the rebound chamber 32.A compression stop 62, preferably of elastomeric material, is mounted onthe piston rod 58 between the second end 55 of the housing 52 and a stopmember 64 secured to the piston rod. In an alternative arrangement, thecompression stop could be positioned in the compression chamber 30between the piston 34 and the floating piston 35.

The rebound stop 60 restricts axial movement of the piston 34 towardsthe second end 55 of the housing 52 during rebound movement of thedamper 24 by providing a spring stiffness effect on the movement. Thecompression stop 62 restricts axial movement of the piston 34 towardsthe first end 54 of the housing 52 during compression movement of thedamper 24 by providing a spring stiffness effect on the movement. Withthis arrangement, the characteristics of the torsion bar 22 are changedfrom a passive spring to a spring and damper acting together, asillustrated in FIG. 9, where spring 90 is the spring stiffness effect ofthe torsion bar 22, spring 92 is the spring stiffness effect of the stop60 or 62, and damper 94 is the damping coefficient effect of the damper24. Such an arrangement improves roll damping without affecting heavedamping characteristics. The damping characteristics of the rebound stop60 and the compression stop 62 are predetermined dependent on vehiclerequirements, and can be adjusted by changing the material and/orproperties and/or shape of the stops. For example, the elastomeric stops60, 62 may be replaced by metallic coil springs, such as titaniumsprings.

FIG. 4 shows a second embodiment of roll control system 200 inaccordance with the present invention which is substantially identicalto the first embodiment, except that the rigid-arm has been replaced bya second damper 24. The two dampers 24 are substantially identical.

FIG. 5 shows a third embodiment of roll control system 20′ in accordancewith the present invention which is substantially identical to the firstembodiment. In this third embodiment, the valve arrangement of thedamper 24′ has been replaced by a solenoid actuated valve 36′ (FIG. 6)which is electrically connected to a control unit 26 by a line 40.

The control unit 26 is preferably a microprocessor which receivessignals from one or more sensors (such as a vehicle speed sensor 42, atransmission speed sensor 44, a steering wheel angle sensor 46, and/or adriver preference switch 48) monitoring certain vehicle conditionsand/or driver preference. The control unit 26 controls the actuation ofthe valve 36′, and hence controls the flow of hydraulic fluid betweenthe compression chamber 30 and the rebound chamber 32, dependent on thesignals received from the sensors and driver preference switch, and mayalso actuate an alarm, such as a warning light 50, inside the vehicle 10during certain monitored conditions. The presence of the control unit 26and the electrically controlled valve 36′ provide the option of asemi-active roll control system in which the damping characteristics ofthe damper 24′ may be adjusted dependent on predetermined vehicleconditions.

FIG. 7 shows a fourth embodiment of roll control system 20″ inaccordance with the present invention which is substantially identicalto the first embodiment. In this fourth embodiment, the fluid in thecompression chamber 30 and the rebound chamber 32 is amagnetorheological fluid, and the valve arrangement comprises an orifice39 in the piston 34, with an associated viscosity control device 36″mounted on the piston 34 (FIG. 8). The control device 36″ creates avariable magnetic field on the fluid in the orifice 39, and iselectrically connected to a control unit 26′ by a line 40′.

The control unit 26′ is preferably a microprocessor which receivessignals from one or more sensors (such as a vehicle speed sensor 42, atransmission speed sensor 44, a steering wheel angle sensor 46, and/or adriver preference switch 48) monitoring certain vehicle conditionsand/or driver preference. The control unit 26′ controls the actuation ofthe control device 36″, and hence controls the viscosity of themagnetorheological fluid as the fluid passes between the compressionchamber 30 and the rebound chamber 32, dependent on the signals receivedfrom the sensors and driver preference switch, and may also actuate analarm, such as a warning light 50, inside the vehicle 10 during certainmonitored conditions. The presence of the control unit 26′, themagnetorheological fluid, and the control device 36″ provide the optionof a semi-active roll control system in which the dampingcharacteristics of the damper 24″ may be adjusted dependent onpredetermined vehicle conditions, up to the point of locking of thedamper 24″.

Alternative arrangements for the above described embodiments for the oreach damper 24 may be used. For example, the mounting arrangement of thedamper 24 may be reversed with the piston rod 58 attached to thesuspension unit 18 and the housing 52 attached to the torsion bar 22.

The present invention provides a roll control system in which thepassive spring of a standard torsion bar is replaced by a spring anddamper acting together, thereby providing an improved passive rollcontrol system. The roll control system can be easily altered to providea semi-active roll control system by controlling fluid flow between thecompression and rebound chambers.

1. A roll control system for installation between axially aligned wheelsof a motor vehicle, the roll control system comprising a torsion bar; adamper attached to one end of the torsion bar and attachable to one ofthe wheels; and attachment means attached to the other end of thetorsion bar and attachable to the other wheel; wherein the dampercomprises an axially extending cylindrical housing; a piston slidablymounted inside the housing; a piston rod connected to the piston,extending out of one end of the housing, and movable in an axialdirection relative to the housing; a floating piston slidably mounted inthe housing between the piston and the other end of the housing; acompensation chamber between the floating piston and the other end ofthe housing containing a first pressurised fluid; a compression chamberbetween the floating piston and the piston containing a secondpressurised fluid; a rebound chamber between the piston and the one endof the housing containing the second pressurised fluid; valve means onthe piston allowing restricted flow of the second pressurised fluidbetween the compression chamber and the rebound chamber; a rebound stoppositioned in the rebound chamber between the piston and the one end ofthe housing and providing a spring-effect on the movement of the pistontowards the one end of the housing; and a compression stop providing aspring-effect on the movement of the piston towards the floating piston.2. A roll control system as claimed in claim 1, wherein the compressionstop is positioned around the piston rod outside of the housing betweena stop member secured to the piston rod and the one end of the housing.3. A roll control system as claimed in claim 1, wherein the compressionstop and/or the rebound stop is formed from elastomeric material.
 4. Aroll control system as claimed in claim 1, wherein the compression stopand/or the rebound stop is a metallic spring.
 5. A roll control systemas claimed in claim 1, wherein the first pressurised fluid is nitrogen.6. A roll control system as claimed in claim 1, wherein the secondpressurised fluid is hydraulic fluid.
 7. A roll control system asclaimed in claim 1, wherein the valve means is electronically actuated;the system further comprising an electronic control unit monitoring oneor more predetermined signals, the control unit being electricallyconnected to the valve means to control the flow of the secondpressurised fluid between the compression chamber and the reboundchamber dependent on the monitored predetermined signals.
 8. A rollcontrol system as claimed in claim 7, wherein the valve means is asolenoid valve.
 9. A roll control system as claimed in claim 1, whereinthe second pressurised fluid is a magnetorheological fluid; and whereinthe valve means is an electrically actuated viscosity control device;the system further comprising an electronic control unit monitoring oneor more predetermined signals, the control unit being electricallyconnected to the control device to control the viscosity of themagnetorheological fluid passing between the compression chamber and therebound chamber dependent on the monitored predetermined signals.
 10. Aroll control system as claimed in claim 7, wherein the control unit is amicroprocessor which is electrically connected to, and receives thepredetermined signals from, one or more sensors mountable on the vehicleand monitoring predetermined vehicle operating conditions, and/or adriver preference switch.
 11. A roll control system as claimed in claim1, wherein the attachment means comprises a second damper, the twodampers being substantially identical.
 12. A roll control system asclaimed in claim 1, wherein the attachment means is a rigid arm.
 13. Aroll control system as claimed in claim 1, wherein the piston rod of theor each damper is attached to the torsion bar.
 14. A roll control systemas claimed in claim 2, wherein the compression stop and/or the reboundstop is formed from elastomeric material.
 15. A roll control system asclaimed in claim 2, wherein the compression stop and/or the rebound stopis a metallic spring.